The present invention relates to a manufacture of tobacco-containing smoking articles, and, in particular, to making of such articles whose physical properties can be adjusted, thereby modifying their combustion properties so as to permit control of tar delivery by the article during smoking.
Commonly assigned copending application Ser. No. 148,124, filed May 9, 1980, discloses tobacco-containing smoking articles wherein tar delivery during combustion is controlled by adjusting the density, porosity, surface area and/or composition of the article. These smoking articles are described in such copending application as comprising a coherent mass of combustible tobacco material. The mass of combustible material is further described as having at least one through passage extending from a first opening in the mass surface to a second opening remote from the first and as being of a density and porosity such as to substantially occlude gas flow therethrough, while also being of a porosity sufficient to support combustion of the mass when ignited.
Smoking articles having characteristics as abovedescribed, allow for control of tar delivery as a result of their controlled influence on pyrolysis which is the primary cause of tar production. Pyrolysis may be defined as the thermal evolution of tars and gases by heat produced from the combustion of a carbonaceous incandescent coal. As pyrolysis reduces smoking material to its carbonaceous skeleton, the carbonaceous remains, in turn, combust and provide heat for further pyrolysis of fresh material located adjacent to the combusting material.
As compared to smoking articles of the aforesaid copending application, conventional smoking articles of the type comprising shredded tobacco leaf, shredded reconstituted tobacco sheet, tobacco stems and combinations thereof do not provide similar pyrolysis control. In such conventional articles, a relatively large surface area is available for pyrolysis, and the latter occurs due to the heat of conduction and radiation from the coal, as well as due to heat transferred to noncombusted tobacco adjacent the coal by gases heated by passage through the coal.
Additionally, conventional smoking articles of the above-mentioned type effect different temperature control of heated gases as they progress down the article. Thus, in conventional articles substantial heat dissipation occurs in regions immediately adjacent the coal, thereby reducing the heat of such gases to the point where they no longer can be used to effect thermal release of flavorants downstream of the coal. However, with the articles of the aforesaid copending application, heat reduction is significantly less, thereby permitting downstream thermal flavorant release.
It is an object of the present invention to provide a method for making tobacco articles of the type described in the aforesaid copending application.